8 New NGK IRIDIUM IX Spark Plugs UR4IX # 7401 Extreme performance upgrade over OEM spark plugs and provide a 40,000 to 50,000 mile service life. Plugs feature a fine-wire Iridium center electrode and Nickel-alloy ground electrodes for maximum engine horsepower and torque. Designed for fuel-injected and turbocharged engines. Precision laser-welded electrode construction. Trivalent Metal Plating has superior anti-corrosion and anti-seizing properties.